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BSNL TTA Practice Paper on Electrostatics (Junior Engineer - JE)

1. The force between two charges is 120 N. If the distance between the charges is doubled, the force will be
(a) 60 N
(b) 30 N
(c) 40 N
(d) 15 N

Answer: B

2. The electric field intensity at a point situated 4 metres from a point charge is 200 N/C. If the distance is reduced to 2 metres, the field intensity will be
(a) 400 N/C
(b) 600 N/C
(c) 800 N/C
(d) 1200 N/C

15. An electrolytic capacitor can be used for
(a) D.C. only
(b) AC. only
(c) both D.C. as well as A.C.

Answer: A

16. The capacitance of a capacitor is not affected by
(a) distance between plates
(6) area of plates
(c) thickness of plates
(d) all of the above

Answer: C

17. Which of the following is not a vector ?
(a) Linear momentum
(b) Angular momentum
(c) Electric field
(d) Electric potential

Answer: B

18. Two plates of a parallel plate capacitor after being charged from a constant voltage source are separated apart by means of insulated handles, then the
(a) Voltage across the plates increases
(b) voltage across the plates decreases
(c) charge on the capacitor decreases
(d) charge on the capacitor increases

Answer: B

19. If A.C. voltage is applied to capacitive circuit, the alternating current can flow in the circuit because
(a) varying voltage produces the charg¬ing and dicharging currents
(b) of high peak value
(c) charging current can flow
(d) discharge current can flow

Answer: A

20. Voltage applied across a ceramic dielectric produces an electrolytic field 100 times greater than air. What will be the value of dielectric constant ?
(a) 50
(6) 100
(c) 150
(d) 200

Answer: B

21. Which of the following statements is correct ?
(a) Air capacitors have a blackband to indicate the outside foil
(6) Electrolytic capacitor must be con¬nected in the correct polarity
(c) Ceramic capacitors must be con¬nected in the correct polarity
(d) Mica capacitors are available in capacitance value of 1 to 10 pF

Answer: B

22. The dissipation factor of a good dielectric is of the order of
(a) 0.0002
(b) 0.002
(c) 0.02
(d) 0.2

Answer: A

23. "The total electric flux through any closed surface surrounding charges is equal to the amount oflcharge enclosed".
The above statement is associated with
(a) Coulomb's square law
(b) Gauss's law
(c) Maxwell's first law
(d) Maxwell's second law

Answer: B

24. Three capacitors each of the capacity C are given. The resultant capacity 2/3 C
can be obtained by using them
(a) all in series
(b) all in parallel
(c) two in parallel and third in series with this combination
(d) two in series and third in parallel across this combination

Answer: C

25. For which of the following parameter variation, the capacitance of the capacitor remains unaffected ?
(a) Distance between plates
(b) Area of the plates
(c) Nature of dielectric
(d) Thickness of the plates

Answer: D

26. Which of the following statement is true ?
(a) The current in the discharging capacitor grows linearly
(b) The current in the dicharging capacitor grows exponentially
(c) The current in the discharging capacitor decays exponentially
(d) The current in the discharging capacitor decreases constantly

28. In a capacitor the electric charge is stored in
(a) metal plates
(b) dielectric
(c) both (a) and (6)
(d) none of the above

Answer: B

29. Which of the following materials has the highest value of dielectric constant?
(a) Glass
(b) Vacuum
(c) Ceramics
(d) Oil

Answer: C

30. Which of the following capacitors will have the least variation ?
(a) Paper capacitor
(b) Ceramic capacitor
(c) Silver plated mica capacitor
(d) None of the above

Answer: C

31. Which of the following statements is incorrect ?
(a) The leakage resistance of ceramic capacitors is generally high
(b) The stored energy in a capacitor decreases with reduction in value of capacitance
(c) The stored energy in a capacitor increases with applied voltage
(d) A wire cable has distributed capacitance between the conductors

33. The sparking between two electrical contacts can be reduced by inserting a
(a) capacitor in parallel with contacts
(6) capacitor in series with each contact
(c) resistance in line
(d) none of the above

Answer: A

34. In the case of a lossy capacitor, its series equivalent resistance value will be
(a) small
(b) very small
(c) large
(d) zero

Answer: C

35. The power dissipated in a pure capacitor is
(a) zero
(6) proportional to applied voltage
(c) proportional to value of capacitance
(d) both (b) and (c) above

37. When a dielectric slab is introduced in a parallel plate capacitor, the potential difference between plates will
(a) remain uncharged
(b) decrease
(c) increase
(d) become zero

Answer: B

38. Capacitance increases with
(a) increase in plate area and decrease in distance between the plates
(b) increase in plate area and distance between the plates
(c) decrease in plate area and value of applied voltage
(d) reduction in plate area and distance between the plates

Answer: A

39. A capacitor consists of
(a) two insulators separated by a con¬ductor
(b) two conductors separated by an in¬sulator
(c) two insulators only
(d) two conductors only

45. A capacitor in a circuit became hot and ultimately exploded due to wrong con¬nections, which type of capacitor it could be ?
(a) Paper capacitor
(b) Ceramic capacitor
(c) Electrolytic capacitor
(d) Any-of the above

Answer: C

46. Energy stored in the electric field of a capacitor C when charged from a D.C source of voltage V is equal to joules
(a) CV2
(b) C2V
(c) CV2
(d) CV

51. The capacitor preferred for high frequency circuits is
(a) air capacitor
(b) mica capacitor
(c) electrolytic capacitor
(d) none of the above

Answer: B

52. The capacity of capacitor bank used in power factor correction is expressed in terms of
(a) kW
(b) kVA
(c) kVAR
(d) volts

Answer: C

53. While testing a capacitor with ohm-metre, if the capacitor shows charging, but the final resistance reading is appreciably less than normal, it can be concluded that the capacitor is
(a) short-circuited
(b) open circuited
(c) alright
(d) leaky

55. Which capacitor will be physically smaller for the same ratings ?
(a) Ceramic capacitor
(b) Paper capacitor
(c) Both will be of equal size
(d) None of the above

Answer: A

56. What is the value of capacitance that must be connected in parallel with 50 pF condenser to make an equivalent capacitance of 150 pF ?
(a) 50 pF
(b) 100 pF
(c) 150 pF
(d) 200 pF

Answer: B

57. A mica capacitor and a ceramic capacitor both have the same physical dimensions. Which will have more value of capacitance ?
(a) Ceramic capacitor
(b) Mica capacitor
(c) Both will have identical value of capacitance
(d) It depends on applied voltage

61. The value of dielectric constant for vacuum is taken as
(a) zero
(b) 1
(c) 4
(d) 10

Answer: B

62. Which of the following capacitors is marked for polarity ?
(a) Air
(b) Paper
(c) Mica
(d) Electrolytic

Answer: D

63. Which of the following capacitors can be used for temperature compensation ?
(a) Air capacitor
(b) Ceramic capacitor
(c) Paper capacitor
(d) None of the above

Answer: B

64. Which of the following statements is incorrect ?
(a) The thinner the dielectric, the more the capacitance and the lower the voltage breakdown rating for a capacitor .
(b) A six dot mica capacitor colour coded white, green, black, red and yellow has the capacitance value of 500 pF
(c) Capacitors in series provide less capacitance but a higher voltage breakdown rating for the combina¬tion
(d) A capacitor can store charge be¬cause it has a dielectric between two conductors

69. "The surface integral of the normal component of the electric displacement D over any closed surface equals the charge enclosed by the surface".
The above statement is associated with
(a) Gauss's law
(b) Kirchhoff s law
(c) Faraday's law
(d) Lenz's law

89. The value of E within the field due to a point charge can be found with the help of
(a) Faraday's laws
(b) Kirchhoff s laws
(c) Coulomb's laws
(d) none of the above

Answer: C

90. at a point may be defined as equal to the lines of force passing normally through a unit cross section at that point.
(a) Electric intensity
(6) Magnetic flux density
(c) Electric flux
(d) None of the above

Answer: A

91. Electric intensity at any point in an electric field is equal to the at that point.
(a) electric flux
(b) magnetic flux density
(c) potential gradient
(d) none of the above

Answer: C

92. Electric displacement is a______quantity.
(a) scalar
(b) vector
(c) both of the above
(d) none of the above

100. The time constant of an R-C circuit is defined as the time during which capacitor charging voltage actually rises to ______ percent of its______value.
(a) 37, initial
(b) 63.2, initial
(c) 63.2, final
(d) 37, final

Answer: C

101. The time constant and R-C circuit may also be defined as the time during which the charging current falls to ______ percent of its initial maximum value,
(a) 37
(b) 42
(c) 63
(d) 73

Answer: A

102. The capacitance of a capacitor is influenced by
(a) plate area
(b) plate separation
(c) nature of dielectric
(d) all of the above
(e) none of the above

Answer: D

103. A capacitor consists of two
(a) ceramic plates and one mica disc
(b) insulators separated by a dielectric
(c) silver-coated insulators
(d) conductors separated by an insulator

105. Dielectric strength of a material depends on
(a) moisture content
(b) temperature
(c) thickness
(d) all of the above
(e) none of the above

Answer: D

106. What will happen to an insulating medium if voltage more than the breakdown voltage is applied on it ?
(a) It will become magnetic
(b) It will melt
(c) It will get punctured or cracked
(d) Its molecular structure will get changed

109. One volt is the same as
(a) one joule/coulomb
(b) one coulomb/joule
(c) one coulomb
(d) one joule

Answer: A

110. The capacitance between two plates increases with
(a) shorter plate area and higher ap¬plied voltage
(6) shorter plate area and shorter dis¬tance between them
(c) larger plate area, longer distance between plates and higher,applied voltage
(d) larger plate area and shorter distance between plates

Answer: D

111. The capacitance C is charged through a resistance R. The time constant of the charging circuit is given by
(a) CIR
(b) 1/RC
(c) RC
(d) RIC

Answer: C

112. The bridge used for the measurement of the value of the capacitance is
(a) Wien's bridge
(b) Wheatstone bridge
(c) Schering bridge
(d) Hay's bridge

114. Out of the following capacitors of identical rating which one will have the smallest dimensions ?
(a) Aluminium foil capacitor
(b) Mica capacitor
(c) Ceramic capacitor
(d) Paper capacitor

Answer: C

115. An uncharged conductor is placed near a charged conductor, then
(a) the uncharged conductor gets charged by conduction
(6) the uncharged conductor gets charged by induction and then attracted towards the charging body
(c) the uncharged conductor is attracted first and then charged by induction
(d) it remains as such

Answer: B

116. The presence of an uncharged conductor near a charged one increases the
(a) charge of the charged conductor
(6) capacity of the charged conductor
(c) potential of the charged conductor
(d) all of the above

119. A potential of 400 V is applied to a capacitor, the plates of which are 4 mm apart. The strength of electric field is
(a) 100 kV/m
(b) 10 kV/m
(c) 5 kV/m
(d) 2 kV/m

Answer: A

120. For a good 0.05 uF capacitor ohmmeter reading should
(a) show low resistance momentarily and back off to a very high resis¬tance
(6) show high resistance momentarily and then a very low resistance
(c) go quickly to 50 ohm approximately and remain there
(d) not move at all

Answer: A

121. The ohmmeter reading for a short circuited capacitor is
(a) infinity
(b) few kilo ohms
(c) few megaahms
(d) zero

Answer: D

122. Which of the following statements is correct ?
(a) Mica capacitors are available in capacitance values of 5 to 20 \iF
(b) Air capapitors have a black band to indicate the outside foil
(c) Electrolytic capacitors must be connected in correct polarity
(d) Ceramic capacitors must be con¬nected in correct polarity

Answer: C

123. Which of the following capacitors preferred for high frequency circuits ?
(a) Air capacitor
(b) Electrolytic capacitor
(c) Mica capacitor
(d) none of the above

126. If a third equal and similar charge is placed between two equal and similar charges, then this third charge will
(a) move out of the field of influence of the two charges
(b) remain in stable equilibrium
(c) not be in equilibrium
(d) be in unstable equilibrium

Answer: B

127. A region around a stationary electric charge has
(a) an electric field
(b) a magnetic field
(c) both (a) and (b)
(d) none of the above

Answer: A

128. The minimum value of potential gradient in a cable occurs in
(a) insulation
(b) conductor
(c) outer sheath
(d) uniformly all over

Answer: A

129. Dielectric strength of medium
(a) increases with rise in temperature
(b) increases with moisture content
(c) is same for all insulating materials
(d) none of the above

Answer: D

130. A charge which when placed in vacuum from an equal and similar charge repels with a force of 9 x 109 N, is known as
(a) milli-coulomb
(b) micro-coulomb
(c) pico-coulomb
(d) coulomb

132. A positive and a negative charge are initially 50 mm apart. When they are moved close together so that they are now only 10 mm apart, the force between them will be
(a) 5 times smaller than before
(b) 5 times greater than before
(c) 10 times greater than before
(d) 25 times larger than before

Answer: D

133. Which is the most superior dielectric out of the following ?
(a) Air
(b) Glass
(c) Bakelite
(d) Paper

Answer: C

134. When a dielectric is placed in an electric field the field strength
(a) decreases
(b) increases
(c) reduces to zero
(d) remain unchanged

Answer: A

135. To prevent the generation of static charges on rubber or flat leather
(a) surface is moistened
(b) conductive dressing is done
(c) oil compound dressing is done
(d) talcum powder is sprayed on the surface